Came to me a crazy idea connecting all variants by a special campaign.

You start it in AOS with a starting hero fighting tru maps (inheriting properties of unit and maybe the army to each next map)
on end of the campaign there is a Portal you need to go in (aolone with the hero) and lat map is completed wit ha message:
"The portal teleported you tru time to an unknown modern age"
And it will appear in the WW2 game, unlocking the special campaign where the hero is in your starting unitset - maybe a slightly different costume (skin), and you continue tru the campaign, you need to preserve him, and on the end again a Portal thing (maybe a shrine whereyou enter somewhere Egypt, and mapcompletes telling "you fell in a dream of fantasies"
And so you have unlocked a campaign in AOF and so on

crazy right?

but needs some implementation
- inheriting fighting team members tru campaign maps - it was an idea to implement already (optional, since we can start all maps with your hero fully healed and on basic form inheriting nothing, giving new "team")
- making connection of player accounts tru AOS-AOF-AOW
- making a pack on server about the hero in "transfer" (going tru portals)
- inheriting hero stats, hp true game alternatives (optional, since we can start all maps with your hero fully healed and on basic form inheriting nothing)

.......
- inheriting fighting team members tru campaign maps - it was an idea to implement already (optional, since we can start all maps with your hero fully healed and on basic form inheriting nothing, giving new "team")
........

I like this part since i can put some secrets to power up heroes and those power ups if found would come with them through campain.